In optoelectronic devices, e.g., light-emitting diodes (LEDs), silicones are frequently used as casting materials. However, conventional silicones have a low thermal conductivity of approximately 0.2 W/(m*K), which means that in the longer term embrittlement and cracking can occur in the silicone casting compound owing to thermal loading during operation of the device. The luminous efficiency of the device is hereby impaired and the service life thereof is reduced since moisture or harmful gasses can penetrate into the device.
In order to alleviate these disadvantageous effects, spherical SiO2 particles, in particular in the μm range, are optionally added to a casting silicone, whereby the thermal conductivity of the casting compound is moderately increased. Generally, this is less than 0.4 W/(m*K). However, SiO2 particles may require careful adaptation of the refractive index of the silicone since otherwise the luminous efficiency of the device is greatly reduced owing to light scattering. Therefore, it is desirable to provide optoelectronic devices or optical elements which have a further improved thermal conductivity and as far as possible have a small amount of light scattering in the optical element, which permits a high luminous efficiency.